1. Technical Field
The present invention relates to a fog detector mounted to a vehicle, and a method of placing the fog detector.
2. Background Technology
Fog detectors have been known. The fog detectors are designed to detect the density of fog by emitting infrared radiation and receiving reflected infrared radiation reflected by particles of the fog (backscattered light).
One type of the fog detectors can perform a stable detection despite any undesirable surrounding environment. This fog detector comprises a light emitting element that reflected infrared radiation and a light receiving element that receives the emitted infrared radiation. The light emitting element and the light receiving element are placed in such a manner that the light axes of the elements cross each other. The light receiving element is designed to receive only the backscattered light reflected within a predetermined area of the detector. Such fog detector is disclosed, for example, in Japanese Unexamined Patent Publication No. H06-99772.
Retrofitting the fog detector in the vehicle interior has been proposed, instead of installing it to the vehicle bumper at the beginning during manufacturing, or even installing the fog detector in the vehicle interior, for the purpose of easy maintenance, at the beginning during manufacturing has been proposed.
However, because the fog detector installed in the vehicle interior is designed to emit and receive the infrared radiation through a window glass (a front glass or a rear glass), it receives not only backscattered light from the fog but also reflected light from a window glass, particularly when the window glass is obscured with dust, drops of water, or the like.
Because the amount of the reflected light from the window glass is larger than that of the backscattered light from the fog, the backscattered light is buried in the reflected light, inducing the inaccurate detection of the backscattered light.
To solve such problem the window glass has to be separated into two sections, one for passing the emitting light and the other for passing the receiving light so as not to receive the reflected light from the window glass, or in order to maintain the glass surface to accurately reflect the light constantly.
However, the former case requires a particular kind of glass to be used for a front glass or a rear glass, and the latter case requires the glass surface to be maintained constantly. Therefore, both cases are indeed unpractical.